Which part of the following sentence is grammatically incorrect ?
The facts in that complex case is questionable.

Question

Accepted Answer

The grammatically incorrect part of the sentence is "is".

**Explanation:**

The subject of the sentence is "The facts". "Facts" is a plural noun. Therefore, the verb must agree with the plural subject. The singular verb "is" does not agree with the plural subject "facts". The correct verb to use would be "are".

**Why the other options are incorrect:**

*   **Option 1: "the"**: The definite article "the" is used correctly to specify which facts are being referred to (the facts in that complex case). There is no grammatical error in its usage.

*   **Option 2: "in"**: The preposition "in" is used correctly to indicate the location or context of the facts (the facts *in* that complex case). It establishes the relationship between the facts and the case.

*   **Option 3: "that"**: The demonstrative adjective "that" is used correctly to specify which complex case is being referred to. It correctly modifies the noun "case".